The role of neutrophils in the pathogenesis of idiopathic pulmonary fibrosis.

STUDY OBJECTIVES The prognostic value of the neutrophil count in BAL fluid (BALF) has been controversial. The role of neutrophils in this inflammatory lung disease, therefore, was evaluated in this study by additional measures. MATERIALS AND METHODS We performed BAL in 22 patients with idiopathic pulmonary fibrosis (IPF) diagnosed by open lung biopsy specimen. Percent polymorphonuclear leukocyte (PMN) in BALF and absolute neutrophil counts were compared with those of normal nonsmokers. Elastase complexed to alpha-1-proteinase inhibitor (alpha1-PI) in plasma and BALF was measured as a marker of elastase burden, and neutrophil distribution in 22 lung tissues was observed by immunohistochemistry using antineutrophil elastase antibody. RESULTS Percent PMN and absolute neutrophil counts in BALF did not increase in patients with IPF as compared with normal nonsmokers (n=15); the plasma elastase-alpha1-PI complex value (mean+/-SE) of patients with IPF (668.5+/-112.4 ng/mL) was significantly high as compared with that of normal nonsmokers (130.3+/-21.3, p<0.001). In addition, the BALF elastase-alpha1-PI complex value (mean+/-SE) of patients with IPF was also significantly high (333.1+/-87.0 ng/mg albumin) as compared with that of normal nonsmokers (83.1+/-29.3 ng/mg albumin, p<0.05). Immunohistochemistry demonstrated considerable numbers of neutrophils infiltrating the lung parenchyma in biopsy specimens obtained by open lung biopsy. CONCLUSIONS These results suggested that although the neutrophil count in BALF could not represent the distribution of neutrophil in the lung, high levels of neutrophil elastase were demonstrated in lung parenchyma and also in both BALF and sera. Therefore, neutrophils might indeed play an important role in the pathogenesis of IPF.